In every other study material I am told to put the vapor barrier on the warm side of insulation. The only exception is ncarbs 4.0 BDCS question 9 attached below. I answered C. They say to put the barrier between 2 pieces of sheeting - why?

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You put a vapor barrier on a rigid surface, not directly on the insulation. So, the sheathing would be secured on the outside of the insulation and would serve as a rigid surface to which you can then adhere the vapor barrier.

It’s D because thats the closest location to the warm side. I’m in Florida. It’s typically 20 degrees warmer outside than inside. Here, you always want the vapor barrier as close to the outside as possible. With stucco buildings the exterior paint becomes the vapor barrier. You want to stop the moisture at its source.

depends on the region...cold northern would be A because moisture travels from hot to cold...would have to pass through insulation in northern climate and soak it. In south the opposite is true. Moisture would go from outside to inside.